The surface-near area of the ground is in many regions of the world contaminated with foreign bodies as a result of industrialization and military activities. Thus, e.g. throughout the world there are large areas which are contaminated with mines, unexploded shells and other still dangerous war material. In particular plastic mines, which as a result of their low price have been buried or covered with soil in inhabited and uninhabited areas by the warring parties, represent a constant danger for the life and limb of humans and animals.
The ground is often impregnated and/or covered with splinters, projectiles, cartridge cases and other metallic articles such as nails, bottle and can closures, etc., which comparatively speaking are less dangerous.
Plastic mines, mainly designed as anti-personnel mines, are particularly vicious, because they are very difficult to refind. Normally they are close to the ground surface, e.g. being concealed in vegetation such as grass, but are generally buried to a depth of 10 to 15 cm. Plastic mines are generally largely made from plastic and may be completely free from metal. However, in many plastic mines small parts such as igniters are made from metal. At present search methods specifically responding to plastic are unavailable. Therefore plastic mines are frequently detected with the aid of metal probes on the basis of the metal parts in such mines.
Metal-free mines cannot be found by means of metal probes. The effectiveness of the search for plastic mines with the aid of metal probes is consequently greatly impaired by the fact that sensitive metal probes respond to any metal parts without it being possible to directly gather from the search signal what type of metal is involved, how large the metal fragment is and whether it is a harmless metallic fragment, nail, crown cork, etc. or a metal part of a plastic mine. Only in the latter case would evacuation and/or rendering safe operations be necessary. To increase the efficiency in the search and elimination of mines, it is therefore necessary to reduce the false alarm rate.
The problem of the invention is to provide a method and a device making it possible to differentiate harmless metal parts concealed close to or in the ground from in particular plastic mines. Preferably it is also to be possible to identify plastic mines on the basis of their type.